The locomotive is opened via the screw clearly visible from above on the dome in front of the cab:

The locomotive presents itself as a classic analog Märklin locomotive with a universal motor and uncoupler. A detailed guide for locomotives of this type can be found in the article Conversion E103 Märklin 3054.

The wires are removed from the guides. This photo documents the condition before you begin desoldering wires:

Now the switch is removed. The old radio interference suppression coil and the capacitor between the motor and housing are no longer needed:

Then, from the accessories for locomotive conversion H0a (CTC No. P2-12-01), the ferrite coil (3.3 uH) is soldered to the open motor pole. The other end of the coil will later be connected to the motor output of the CTC module.

The field coil remains connected at the other motor pole. Two diodes with different forward directions are connected to the connections that were previously linked to the switch. The other ends of the two diodes are connected together and later connected to the motor output of the CTC module.

Since the front and rear lights are not connected to the locomotive housing, a diode can be omitted for these.

In the following image, the CTC Locomodule H0a and the support capacitor have been tentatively placed:

Now the motor, the light, both uncouplers, and the support capacitor are soldered to the CTC module. The wire on the negative pole of the support capacitor is used as the common GND point.

In the following image, the CTC module and the support capacitor are installed. Motor (purple wire), light (yellow and brown wires), and uncoupler (gray wires) are connected:

Now only the IR receiver is missing. With the BR86, it is convenient to fix it on the mount of the front wheelset:

The cable of the IR receiver fits through the same slot as the cables of the front uncoupler.

Here you can see the fully installed IR receiver: